In the extraction of hydrocarbons such as oil and gas from underground formations, it is common practice to drill a borehole from the surface to the hydrocarbon bearing formation. Such formations often have significant horizontal extent but are of limited vertical extent. Thus, to optimise the amount of hydrocarbon extracted, it is desirable to optimise the path of the borehole through the formation. In recent years, the drilling of non-vertical boreholes (often called ‘deviated’ or ‘horizontal’ boreholes) in hydrocarbon formations has been undertaken for this reason. However, in certain cases, only a ‘vertical’ borehole is available. For example, an old borehole drilled before deviated drilling procedures were developed might pass through a hydrocarbon formation for only a short path. In other cases, the original well may have bypassed formations containing hydrocarbons. One way to improve hydrocarbon recovery in such cases is to drill further, ‘lateral’ boreholes from the main borehole into the formation(s) of interest.
Using traditional drilling methods, the technique for drilling lateral borehole comprises setting a whipstock in the well at the desired location and using the whipstock to cause a drill bit on a drill string to drill into the sidewall of the borehole to create the lateral borehole. Once the lateral is drilled, the drill string is withdrawn from the borehole and the whipstock must be recovered. If it is desired to drill several laterals, the whipstock must be repositioned and withdrawn each time. Thus the process is slow and expensing, as it requires the presence of a drilling rig or a coiled tubing drilling unit to perform these operations.
WO2004072437 A discloses an electric drilling machine that can be run on wireline cable. The drilling machine carries a kick plate which it orients prior to drilling to force the drill bit in the desired direction to drill the lateral. The mechanism for connecting the kick plate to the drilling machine and for orienting it to drill in the desired direction is relatively complex.
This invention provides a simpler approach by supporting a guide on the drill string and orienting the guide by rotating the drill string with the drilling machine.